Linear permissions have been proposed as a lightweight way to specify how an object may be aliased, and whether those aliases allow mutation. Prior work has demonstrated the value of permissions for addressing many software engineering concerns, including information hiding, protocol checking, concurrency, security, and memory management. We propose the concept of a permission-based programming language--a language whose object model, type system, and runtime are all co-designed with permissions in mind. This approach supports an object model in which the structure of an object can change over time, a type system that tracks changing structure in addition to addressing the other concerns above, and a runtime system that can dynamically check permission assertions and leverage permissions to parallelize code. We sketch the design of the permission-based programming language Plaid, and argue that the approach may provide significant software engineering benefits.